The metabolism of the corticosteroid side chain is being studied in man and animals. The objectives are to determine the significance of pathway of oxidative metabolism which results in the formation of steroidal carboxylic acids. In humans, steroidal 20-hydroxy-21-oic acids derived from cortisol are excreted in the urine. Enzymes have been isolated from hamster liver which catalyze the enolization of the ketol side chain, and net oxidation of the ketol side chain of 11-deoxycorticosterone to 20-oxo-21-oic acids and 20-hydroxy-21-oic acids. A new pathway for reduction of cortisol to hexahydro metabolites and which by-passes tetrahydrocortisol in humans is under study.